Keeping trim: A new survey has revealed that half of men would dump a girlfriend if she gained weight - but only 20 per cent of women would do the same.

Step away from that cookie if you want to keep your boyfriend, ladies.

A new survey has found that nearly half of men would dump a woman who gained too much weight.

The poll, of 70,000 people across the US showed that 48 percent of men would not want to be with their partner if she became fat.

By contrast just 20 percent of women would stop seeing their man when faced with the situation.

The poll found that over a third of men believed that women started to loose their looks at the age of 40, while a quarter believe that a woman is beyond her prime after 50. The same was true of women, though a further 23 percent believe a man will never lose his looks.

The poll also found that men were more likely to lie about the number of sex partners they had been with, and 42 percent said that they would consider a woman sexuallypromiscuousif she had slept with over 10 men.

By contrast, almost the same number of women said that they would consider a man overly promiscuous after 20 sexual partners.

18 percent admitted they had told a woman he loved her for the sole purpose of sleeping with them.